Vermont police have finally cracked the cold case of the murder of a 24-year-old school teacher that happened 52 years ago with help from DNA forensics technology and one piece of evidence — a discarded cigarette butt.

Burlington Police said the DNA evidence from a cigarette left at the crime scene led investigators to an upstairs neighbor who strangled Rita Curran to death after fighting with his wife on a July night in 1971.

According to police, the suspect is William DeRoos, who was 31 at the time of the murder.

The killing took place during a 70-minute window, after which DeRoos told his wife he was taking a “cool-down walk.” He then told his wife — who he had been married to for only two weeks — not to say that he had been out.

One of Curran’s roommates discovered Curran’s body after he returned and called police. Investigators at the time said Curran resisted fiercely.

The investigation was brought back to life in 2019, and a repeated interview with DeRoos’ former wife was conducted. This time, she stated that DeRoos had left the apartment for a short time while Curran’s roommates were gone.

Police said the case will now finally be closed.

“We’re all confident that William DeRoos is responsible for the aggravated murder of Rita Curran, but because he died in a hotel room of a drug overdose, he will not be held accountable for his actions, but this case will be closed,” Burlington Police Detective Lieutenant James Trieb, the commander of the Detective Services Bureau, said during a recent news conference.

DeRoos, who styled himself as a guru, moved to Thailand to become a monk but later returned to the United States. He died of a drug overdose in San Francisco in 1986.

Curran’s parents have already passed away, but Curran’s brother and sister attended the event at Burlington police headquarters.

“I don’t think so much about the guy who did this as I do about Rita, my parents and what they went through,” Curran’s brother, Tom, said. “I pray to Rita and I pray to my parents.”

After the case was reopened in 2019, Detective Trieb and a team of investigators and technicians got to work on a key piece of evidence left at the scene — a cigarette butt that was found near Curran’s body.

In 2014, the evidence was sent for DNA analysis but it did not match any samples on law enforcement DNA databases at the time.

Five years later, the detectives contracted with a DNA testing company to compare the samples of genetic material to those from the public compiled by commercial DNA testing companies.

Finally, last August, detectives discovered that the sample had been traced to relatives on both sides of DeRoos’ family.

Although DeRoos’ then-wife, Michelle, told investigators at the time that she had not heard or seen anything, she admitted to investigators in a recent interview that she had lied about her husband leaving.

A later wife of DeRoos also told detectives that he was prone to violent outbursts.

Detective Thomas Chennette, who interviewed DeRoos’ first ex-wife, said he thinks she did not believe her husband was responsible for the murder but was covering for him as he had a criminal record.

“I think she lied at the time because she was young. She was naive. She was newly married. She was in love,” Chennette said.